The Great White Brick - '69 Valiant

I want to put in a V8 k-frame but my buddy (who's going to own the car when we're done) thinks this one is in nice shape and the 318 was sitting on it pretty good so why bother? It had homemade shims under 318 mounts and was sitting well enough that the exhaust wasn't hitting anything. Is a /6 K-frame really that bad?